Analysis of The Causes of Blistering On The Surface of Copper Immersion Plating on PCB Boards (1)

Blistering on the board surface is one of the more common quality defects in the production process of circuit boards. Because of the complexity of the circuit board production process and the complexity of process maintenance, especially in the chemical wet treatment, the prevention of blistering defects on the board surface is difficult. Based on many years of actual production experience and service experience, I make a brief analysis of the causes of blistering on the surface of the circuit board immersed copper electroplating. I hope that it can play a role in attracting jade to everyone’s process production and problem-solving!

The blistering on the surface of the circuit board is actually the problem of poor bonding force of the board surface, and the extension is also the problem of the surface quality of the board surface, which includes two aspects: 1. The problem of the cleanliness of the board surface; 2. The surface micro-roughness (or surface energy) problem. The board surface blistering problem on all printed circuit boards can be attributed to the above reasons. The bonding force between the plating layers is poor or too low, and it is difficult to resist the production and processing process in the subsequent production process and assembly process. Coating stress, mechanical stress and thermal stress, etc. generated in the process eventually cause different degrees of separation between the coatings.

Now, some factors that may cause the poor quality of the board surface in the production and processing process are summarized as follows:

1. The problem of substrate processing, especially for some thinner substrates (generally below 0.8mm), because the substrate rigidity is poor, it is not suitable to use a brushing machine to brush the plate, This may not effectively remove the protective layer specially treated to prevent oxidation of the copper foil on the board during the production and processing of the substrate. Although the layer is thin and the brush board is easier to remove, it is difficult to use chemical treatment, so it is important to pay attention to control in production and processing to avoid causing damage to the board surface. The problem of blistering on the board surface is caused by the poor adhesion between the base copper foil and chemical copper. When the thin inner layer is blackened, there will also be problems such as poor blackening and browning, uneven color, and partial blackening and browning.

2. Poor surface treatment due to oil or other liquid contamination and dust contamination during machining (drilling, lamination, milling, etc.).

3. Poor copper sinking brush plate: The pressure of the grinding plate before sinking copper is too large, causing the orifice to deform and brush out the copper foil fillet of the orifice or even the hole to leak the base material, which will cause problems in the process of copper sinking electroplating, spray tin welding, etc. orifice foaming phenomenon. Even if the brush plate does not cause leakage of the base material, the overweight brush plate will increase the roughness of the copper in the orifice, so the copper foil at this place is prone to excessive roughening during the micro-etching and roughening process, and there will also be a certain degree of roughness quality risks.
Therefore, attention should be paid to strengthening the control of the brush plate process, and the brush plate process parameters can be adjusted to the best through the wear scar test and the water film test.

4. Washing problem: Because the copper sinking electroplating treatment needs to go through a lot of chemical solution treatment, there are many kinds of acid, alkali, non-polar organic and other chemical solvents, and the surface of the board is not clean, especially the copper sinking adjustment and degreasing agent, which will not only cause cross-contamination. At the same time, it will also cause poor local treatment or poor treatment effect, uneven defects, and cause some problems in bonding force. Therefore, we should pay attention to strengthening the control of washing, mainly including the flow of washing water, water quality, washing time, and the control of the dripping time of the board; especially in winter when the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the control of the washing.